1. Field of the Invention
The present invention relates to a friction device, such as an automotive brake system, particularly as a disc brake assembly. More specifically, the invention relates to compositions of matter for producing a component of the friction device.
2. Description of the Background Art
Automotive disc brakes are designed to convert kinetic energy into thermal energy and dissipate heat generated owing to this conversion to the atmosphere. The disc brake assembly comprises a disc rotor rotatable with a road wheel and a brake pad carried by a caliper cylinder. The brake pad is brought into contact with the disc rotor for frictionally restricting rotation of the disc rotor, thus restricting rotation of the road wheel.
Conventionally, the disc rotor is formed of a material composition as shown in the following table I.
TABLE I ______________________________________ JIS Chemical Composition Tensil Brinell No C Si Mn P S Fe Strength Hardness ______________________________________ FC25 3.35 2.1 0.6 0.02 0.1 Rem 26.4 88.1 ______________________________________
On the other hand, the brake pad is formed of a material composition as shown in the following table II.
TABLE II ______________________________________ Semi- Low Steel Composition Asbestos Metallics Non Steel ______________________________________ Asbestos Fiber 20-50 -- -- Steel Fiber -- 40-70 0-20 Replacement Fiber -- -- 3-30 Organic Matrix 10-20 5-20 5-20 Lubricant 0-20 5-20 0-15 Metal 10-30 5-20 10-30 Others 5-20 10-20 5-40 ______________________________________
In the recent years, because of advancement of the automotive technologies for providing higher performance in various aspect, such as an internal combustion engine as prime mover, a power train, suspension systems, body structures and so forth, as well as extension of highway networks, occurrences of high speed braking is substantially increased. By repeatedly applying high speed braking, a large amount of kinetic energy is converted into thermal energy for heating the components of the brake. Since heat is accumulated owing to increased repetition of high speed braking, the possibility of inducing heat checks is increased.
It may be possible to use material having high thermal conductivity for forming the brake pad. Such high thermal conductivity brake pads may reduce the occurrence of heat checks. However, the high thermal conductivity causes increased amount of heat to be transferred to the caliper cylinder and then to the associated hydraulic brake circuit. This results in increased possibility of the occurrence of vapor lock.